The laws just tell us that the planets all move on elliptical orbits, not circular ones like people used to think for thousands of years before Kepler's discovery. His second law is a bit more complicated, but it describes a special kind of relationship that planets have among each other in terms of how fast they move. If you plotted a planets position on the ellipse, and drew lines from the planet to the location of the Sun at equal instants in time you would get a bunch of triangle-shaped wedges. If you take any pair of these 'equal time interval' wedges and measured its area, you would find that the wedges all have equal areas, thus "Law II : Planets sweep out equal areas in equal times". The third law is one you can also discover yourself by using a table of the planets which shows their distance from the Sun in 'Astronomical Units' and the length of their orbit in 'Earth Years'. If you calculate the 'square of their year' and divide by the 'third power of their distance' you will find that this quantity is a constant for all the planets:
d p
distance period (P x P)/ (D x D x D)
Mercury 0.3870 0.240 0.994
Venus 0.7233 0.615 0.999
Earth 1.0000 1.000 1.000
Mars 1.5237 1.881 1.000
Jupiter 5.2028 11.862 0.999
Saturn 9.5388 29.458 0.999
Uranus 19.1819 84.014 1.000
Neptune 30.0578 164.793 1.000
Pluto 39.44 247.7 1.000
As you see, the 'constant' is very close to the same value to better than 1 percent which confirms Kepler's Third Law. As for its explanation, a proper one requires a bit of physics that is only meaningful to someone that has taken High School physics. Still, some 'Laws' are like that in science. We know what the law is, but sometimes its full explanation has to await the development of the proper theory which may not happen for many years after the Law is discovered.
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